1. Field of the Invention
This invention relates to a method of growing crystals.
2. Description of the Related Art
As a representative example of conventional methods of growing crystals, we describe the method proposed in Japanese Patent Publication No. 1082/1980 (55-1082) with reference to FIG. 5.
In this method, as shown in FIG. 5(a), a solution 1 containing crystalline material is filled in an elongated container 2 like a tube. One end of this container is cooled and the other end is heated to give the test solution a temperature gradient so that crystals would form in a region where the degree of supersaturation is large. FIG. 5(a) describes this method, (b) illustrates the temperature gradient produced in the method, and (c) shows the solubility when the crystalline material is lysozyme.
The solubility of a crystalline material changes with temperature. For example, albumen (egg white) lysozyme changes its saturation solubility with temperature as shown in FIG. 6.
When a crystalline material is dissolved in a solution so as to become supersaturated, the amount of molecules which is in excess beyond the solubility form crystals. If we provide a test solution with some temperature gradient, crystallization begins where the solubility is small. In the region where the concentration exceeds the solubility, even though it may be late to start, crystallization eventually begins.
Because temperature varies moderately according to a conventional method, the degree of supersaturation also changes gradually and crystals form in an extended area. Therefore, the number of crystals is large in comparison with the amount of the crystalline material, and therefore the crystals do not grow sufficiently large.
For example, when a solution which contains 3% of albumen lysozyme (which is a protein) as a crystalline material and 3% of sodium chloride as an auxiliary agent and the pH value of which is adjusted to 4.6 using HCl was placed in a container 2 having a length of 220 mm and an inner diameter of 12 mm and given a linear temperature gradient of 1.3.degree. C./cm which is a result of 7.degree. C. at the cooling end and 35.degree. C. at the heating end, more than 1,000 crystals per centimeter were observed in the portion where the temperature is 20.degree. C. or less and which is not more than 10 cm from the 7.degree. C. cooling end. If the temperature is over 20.degree. C., the number of crystals decreases considerably and no crystals were observed near 30.degree. C.
If we assume that 1,000 pieces per centimeter of crystals formed in the region where the temperature is 20.degree. C. or less and that no crystals formed above 20.degree. C., it can be calculated that 10,000 crystals formed from 0.75 g of albumen lysozyme. Without the temperature gradient, 22,000 crystals can form from 0.75 g of albumen lysozyme. Therefore, while the effect of the added temperature gradient can be recognized, the number of crystals is still large and it is not possible to form dramatically large crystals.